Menu Sign In Contact FAQ
Banner
Welcome to our forums

Another reason to go for a 18000ft transition level?

Now, AFAIK, these are usually delimited in terms of ft agl rather than FL so the issue described by Peter is a non-event in Germany.

Only for airspace borders below 5000 ft. D(not CTR) in EDDG for instance has a top border of 4500 ft MSL and above Marl there is C from EDDL that goes from FL65 to FL100. D(not CTR) of EDDW goes up to FL65.

mh
Aufwind GmbH
EKPB, Germany

We have a similar issue with portable ADS-B receivers that don’t have a built in pressure sensor. They determine altitude by GPS. It is corrected to an equivalent MSL value. However, TIS-B targets are detected by secondary radar and up linked from the ground station and only include the transponder mode C value, which is pressure altitude. So there can be a wide variance between the relative altitude indication. The ForeFlight application improves on this when own ship has ADS-B out as it uses an algorithm to match the ADS-B Own Ship GPS altitude that is broadcast by ADS-B with the portable receiver GPS altitude, latitude and longitude. Once it determines a match, it uses the pressure altitude determined from Own Ship as the comparison parameter with other targets that are being received. ADS-B targets usually have both a pressure altitude and a GPS altitude, so if Own Ship does not have ADS-B Out, the portable GPS altitude is compared with the target GPS altitude, but the ADS-B value is WGS84 and the portable is corrected. This can still introduce an error as they two are not identical, but they are close to each other. Around my neck of the woods, the difference is about 110 feet.

KUZA, United States
I am still positive about installing a ADS-B / Flarm receiver to wire up to EasyVFR for collision avoidance. The TRX 1500 has a GPS sensor (Flarm) that is legal here even for ADS-B OUT, so that is what ATC will see when an S-transponder sends positions info from that. An S-transponder has an altitude encoder inside and that is used for altitude reports via ADS-B. So my question: You don´t fiddle with QNH and altitude corrections on the transponder I guess ? Or do you ? And GPS altitude is ignored by the Transponder ? Vic

P.S. I think ATC does the local QNH adjustment on their screens.

TRX 1500

Last Edited by vic at 04 Mar 17:57
vic
EDME

Do you apply a fixed offset to the GPS altitude, or a linear correction so they both read 0 at sea level (ie, does this compensate for the QNH difference from 1013, or the temp correction)?

In EasyVFR, it’s a fixed offset. So it effectively uses the same altitude as your altimeter for the purpose of generating airspace warnings, be that QNH, QFE or QNE.

EIWT Weston, Ireland
These laptop nav tools are often used for tactical airspace avoidance. They use GPS altitude for that, which isn’t any good if the CAS is defined in terms of a FL.

I see a business opportunity here… A little box with a pressure and temperature sensor that you stick to some unpressurised part of your plane and that tells your tablet app via Bluetooth what the real atmosphere looks like. 9,99 Euros for the parts (2 more for a little solar cell that keeps the battery charged) and 99 Euros bargain retail price in your favorite pilot store: “the poor man’s Air data computer”.

Actually….
this reminds me that Bad Elf now has a BT GPS with baro alti (and another one but even more expensive…) but for more that 99 EUR

Last Edited by PapaPapa at 04 Mar 15:47
ELLX (Luxembourg), Luxembourg

In EasyVFR, we allow the user to “Calibrate” their GPS altitude to their altimeter

Neat idea. GPS-ILS does something similar.

Do you apply a fixed offset to the GPS altitude, or a linear correction so they both read 0 at sea level (ie, does this compensate for the QNH difference from 1013, or the temp correction)?

Last Edited by jwoolard at 04 Mar 15:36
EGEO

In fairness, I don’t think many people will use gps altitude for airspace avoidance.

Where it does come into place, is when pilots are relying on the warning to keep them out of controlled airspace (ie not planning properly). In EasyVFR there is a buffer (and I presume SD and all the other systems) so that if you are approaching an airspace, say 300ft below the base of or above the top of that airspace, you still get the warning. This allows some room for GPS altitude errors.

Of course these errors can be signifiant, especially if you are flying on flight levels, rather than altitude, running the danger of getting no warning that you’re about to enter.

In EasyVFR, we allow the user to “Calibrate” their GPS altitude to their altimeter to minimise the error, to ensure that they still get warnings. It’s as simply a matter of telling EasyVFR the altitude shown on your altimeter, and it will allow for the differences.

EIWT Weston, Ireland

Patrick: You mean C below FL100? Above is not non-complex, above FL100 is trivial. But in general any airspace where you are supposed to set the altimeter to standard is given as FL. That leaves a bit at the far out edges of C/D airspaces and some restricted areas. But in Germany I don’t see any complex airspace structure at all

I mean any airspace for which an inflight tool to increase awareness is useful. In my view, that does not include any airspace boundaries that apply by default in a given area – such as C from FL100.

It is helpful for the reverse wedding cake layers of C above control zones. To put it in a more abstract way: It is useful for any airspace that has both vertical AND horizontal boundaries in a given area. I’m not saying this is awfully complex, in Germany – but it’s helpful to have SykDemon available for such places esp. in non-familiar areas.

Now, AFAIK, these are usually delimited in terms of ft agl rather than FL so the issue described by Peter is a non-event in Germany.

I’m not sure how much airspace in other countries is delimited vertically in terms of FL but jwoolard has already commented on that for UK.

Hungriger Wolf (EDHF), Germany

These laptop nav tools are often used for tactical airspace avoidance. They use GPS altitude for that, which isn’t any good if the CAS is defined in terms of a FL.

I see a business opportunity here… A little box with a pressure and temperature sensor that you stick to some unpressurised part of your plane and that tells your tablet app via Bluetooth what the real atmosphere looks like. 9,99 Euros for the parts (2 more for a little solar cell that keeps the battery charged) and 99 Euros bargain retail price in your favorite pilot store: “the poor man’s Air data computer”.

EDDS - Stuttgart

But kidding apart, how would the value of the transition altitude – 3000, 5000 or 18000ft – have any influence on this “problem”?

because SD shows everything at altitude… so FL 50 is actually shown as 5000ft
But in real life FL 50 can be below 5000ft

So SD can show that at 4800ft you will be below this CAS starting at FL50 when in fact you may be entering it…

if you put TA at 18000 ft then everything CAS under it has to be expressed as altitude and not FL
And most of us won’t fly VFR above 18000ft

Hope i got that right and explained it clearly

ELLX (Luxembourg), Luxembourg
19 Posts
Sign in to add your message

Back to Top